Here's why:

* Largest: The Sun's mass accounts for over 99.8% of the total mass of the entire solar system. This makes it significantly larger than all the planets, moons, asteroids, and comets combined.

* Not the oldest: The Sun formed about 4.6 billion years ago. While that's very old, some of the material that makes up the Sun and the rest of the solar system is even older. This material was formed in previous stars that lived and died before our Sun was born.

So, the Sun is the largest, but not the oldest, object in our solar system.